ON THE PREREQUISITES FOR THE FORMATION OF SOLUTION COMPLEXES FROM [60]FULLERENE AND CALIX[N]ARENES - A NOVEL ALLOSTERIC EFFECT BETWEEN [60]FULLERENE AND METAL-CATIONS IN CALIX[N]ARYL ESTER COMPLEXES

In order to find calix[n]arenes which can interact with [60]fullerene in solution we have screened a number of different calix[n]arenes by s pectroscopic methods. We eventually discovered such three calix[n]aren es (1(5).Bu-t.H, 1(6).Bu-t.H, and 2(3).Bu-t.H) which could accept [60] fullerene even in solution. They commonly possess a cone conformation and a benzene ring inclination suitable to [60]fullerene inclusion. Fu rthermore, it was found that calix[n]aryl ester derivatives, which can not interact with [60]fullerene, become excellent [60]fullerene-accept ors in the presence of certain specific metal cations. This was attrib uted to a metal-induced conformational change to preorganize cone cali x[n]aryl esters. This phenomenon is a sort of positive allosterism, wh ich is the first example in fullerene chemistry. We believe that these findings will open a door to new fullerene-calix[n]arene conjugate ch emistry. (C) 1998 Elsevier Science Ltd. All rights reserved.